C8051T602 View Datasheet(PDF) - Silicon Laboratories
Part Name
Description
MFG CO.
'C8051T602' PDF : 168 Pages View PDF
C8051T600/1/2/3/4/5/6
22.3. Priority Crossbar Decoder
The Priority Crossbar Decoder (Figure 22.3) assigns a priority to each I/O function, starting at the top with
UART0. When a digital resource is selected, the least-significant unassigned Port pin is assigned to that
resource (excluding UART0, which is always at pins P0.4 and P0.5). If a Port pin is assigned, the crossbar
skips that pin when assigning the next selected resource. Additionally, the crossbar will skip Port pins
whose associated bits in the XBR0 register are set. The XBR0 register allows software to skip Port pins
that are to be used for analog input, dedicated functions, or GPIO.
Important note on crossbar configuration: If a Port pin is claimed by a peripheral without use of the
crossbar, its corresponding XBR0 bit should be set. This applies to P0.0 if VREF is used, P0.3 if the exter-
nal oscillator circuit is enabled, P0.6 if the ADC is configured to use the external conversion start signal
(CNVSTR), and any selected ADC or comparator inputs. The crossbar skips selected pins as if they were
already assigned, and moves to the next unassigned pin. Figure 22.3 shows the potential pin assigments
available to the crossbar peripherals. Figure 22.4 and Figure 22.5 show two example crossbar configura-
tions, with and without skipping pins.
Port
P0
All Port 0 pins are capable of being assigned to
Pin Number 0 1 2 3 4 5 6 7 crossbar peripherals.
Special
Function
Signals
The crossbar peripherals are assigned in priority
order from top to bottom, according to this
diagram.
TX0
These boxes represent Port 0 pins which can
RX0
potentially be assigned to a peripheral.
SDA
SCL
CP0
CP0A
Special Function Signals are not assigned by
the crossbar. When these signals are enabled,
the Crossbar should be manually configured to
skip the corresponding port pins.
SYSCLK
CEX0
CEX1
Pins P0.0 through P0.6 can be “skipped” by
setting the corresponding bit in XBR0 to ‘1’.
CEX2
ECI
T0
T1
Pin Skip 0 0 0 0 0 0 0 x
Settings
XBR0
Figure 22.3. Priority Crossbar Decoder Potential Pin Assignments
Rev. 1.2
111
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